Lesions in blood vessels can result from a build-up of an atherosclerotic plaque. The plaque build-up causes a narrowing of the vessel and reduced blood flow therein. In the case of lesions in coronary arteries such reduced blood flow can lead to heart disease and death.
Atherosclerotic lesions can also occur at or near an ostium—the opening of a branching conduit. Ostial lesions damage the ostium of a branching conduit. In aorto-ostial lesions, the treatment outcome using conventional balloon angioplasty has been limited by a low success rate and high incidence of restenosis, or recurrence of artery blockage. An attractive alternative for the treatment of this subset of lesions is coronary stenting.
Coronary stent therapy of aorto-ostial lesions is limited by the need to precisely position the intravascular stent completely within the vascular lumen and as close as possible to the ostium. Limited visualization of the coronary artery ostium, angulations of the aorto-coronary segment and difficulties in the placement of the guiding catheter are all factors that affect the final result. If the stent is not placed far enough into the branch vessel, it extends into the aorta and thus may be subject to trauma from the guiding catheter. In this case, stent protrusion into the aortic lumen interferes with aortic blood flow and hastens further aortic catheterization. On the other hand, if the stent is placed too far into the branch vessel, it may miss the ostium and the tightest portion of the stenosis. In addition, there is the potential to compromise the lumen and subject the patient to a higher incidence of sub-acute stent thrombosis or restenosis, as well as a high risk for dissection, acute closure or rupture.
Various stent placement systems for delivering stents to a vascular lumen immediately adjacent to an ostium are well known in the art. Such systems can utilize a balloon which is inflated around the catheter and used as a positioner against the ostial opening.
For example, U.S. Pat. No. 5,749,890 describes a stent delivery assembly and method for stent placement in an ostial lesion. In particular, the stent delivery system of the invention comprises a break segment which changes configuration to facilitate localization of the target ostium.
Balloon locators can function as a unitary body, however, since such balloons form a fairly rigid structure when inflated, angulation of an attached catheter with respect to an ostium while maintaining full contact between the balloon and the ostial opening, can be difficult if not impossible with such systems. Use of inflatable balloons is also limited by the need for complex inflation mechanisms.
Locators are also known which include individual wire or polymer struts which are extended around the catheter and function as individual stops, each contacting a region of the ostial opening.
For example, U.S. Pat. Appl. Publication No. 2004/181272A1 describes a stent combined with a positioning apparatus to effectively place the stent at a precise deployment site within a narrowed vascular region such as an artery. The stent is maneuvered through the vessel and is guided by a guiding catheter up the vessel to where the narrowing is located. Upon exiting the guiding catheter and approaching the deployment site within the coronary artery, a deployment site locator expands to contact the vascular structure and, thereby, effectively position the stent at the deployment site within the narrowed vessel.
U.S. Pat. Appl. Publication No. 2007/156221A1 describes a stent positioning system, including an inflatable balloon for expanding a stent. The balloon, in its collapsed state, fits into and is adapted to carry the stent in its pre-expanded condition. Stent locator means are slidably accommodated in a guide catheter and adapted to change its shape prior to making contact with the interior wall surface of a major blood vessel in the ostial region of a smaller blood vessel branching off from the major vessel and prior to the expansion of the stent. Mechanical means for changing the shape of the stent locator means are also provided. The change of shape enables the locator means to abut the interior wall surface, thereby ensuring correct apposition between the stent and the ostium of the smaller blood vessel.
Locators in the form of independent and not interconnected loops are also known. For example, U.S. Pat. Appl. Publication No. 2007/173918A1 describes an apparatus and method for locating an ostium of a branch vessel. The apparatus includes a delivery catheter having a distal end sized for introduction into the branch, and locator elements including first ends fixed to the distal end and second ends free from the distal ends. The locator elements can be in the form of loops which are compressible from a transverse, deployed condition to an axial, contracted condition, wherein the second ends are disposed proximal to the first ends. During use, the catheter is directed through a guide catheter into the ostium with the locator elements compressed, and the locator elements are deployed within the branch in the contracted condition. The catheter is partially withdrawn from the branch, the locator elements resiliently expanding towards the deployed condition as they enter the main vessel. The catheter may be used to deliver a stent into the branch with the expanded locator elements facilitating positioning the stent.
Locators with individual strut and loop attempt to overcome the limitations of balloon locators by providing independently movable struts and loops which are mechanically deployed and maintain independent contact with the tissue surrounding the ostium during catheter angulation. Although such configurations can in theory provide better catheter maneuverability, use of individual struts and loops can lead to strut mis-positioning and as a result escape of an individual strut(s) and/or loop(s) into the branch vessel.